Deformation characteristics of Piedmont residual soils

Site investigations conducted at the North Carolina State University Research Farm and adjacent construction sites provided the database to study the soil profile and deformation characteristics of Piedmont residual soil. The database includes both laboratory and in-situ test results. The laboratory testing program was composed of oedometer, stress path, triaxial multistage compression, resonant column, and torsional shear rests. In-situ testing included standard penetration tests, dilatometer tests, and pressuremeter tests with Menard and push-in types. Atypical soil profile is defined based bn Martin's classification system. Test results from triaxial multi-stage compression, resonant column and torsional shear tests show that residual soil's decay pattern of normalized shear modulus with shear strain is similar to and lies between those of sands and San Francisco Bay Mud. The study of soil's compressive stiffness shows that pressuremeter modulus, E(pm) and dilatometer modulus, E(1), are generally consistent while E(N) as correlated from a relationship suggested by Martin between E(pm) and standard penetration test N-value usually lie on the lower bound. Values of reference deformation modulus, E(1), as derived from oedometer tests appeared to be a function of the person who conducted the tests. One tester's results are in good agreement with E(pm) and E(D), while the others are generally much smaller. Due To the difficulty of trimming Piedmont residual soil specimens, one might suggest that the differences in test results are related to sample disturbance on small specimens such as those used in standard oedometer tests.